1. Field of the Invention
The invention relates to a heating system.
2. Related Art Statement
In a system for producing semiconductors, a ceramic heater may be provided for heating a wafer (substrate) so as to deposit a semiconductor thin film on the wafer from gaseous raw materials such as silane gas by means of thermal CVD or the like. A so called 2 zone heater is known as such ceramic heater. Such 2 zone heater has a ceramic substrate and inner and outer resistance heat generators embedded within the substrate. Separate power supply terminals are connected to the respective heat generators so that electric power may be applied independently on the respective generators. The inner and outer heat generators may be thus independently controlled.
Further, in JP-A 5-326112, a resistance heat generator of a ceramic heater is constituted by plural circuit patterns each made of a high melting point metal. The circuit patterns are so arranged that they may supplement one another's defect portions. For example, one of the patterns has a defect portion such as a folded portion or a returning portion. In this case, another circuit pattern is overlapped on or over the defect portion of the one pattern.
For example, in a heater to be used for heating semiconductor wafers, the temperature of the heating surface of the heater needs to be uniformly controlled over the entire surface. It is required that the heater satisfy a severe specification, for example, that the temperature measured on the heating surface is within ±5° C., of the average of the whole heating surface under a use condition.